Correlation methods of room impulse responses for chamber-based sound insulation measurements

Abstract

Sound insulation of building elements, such as walls, doors and windows are quantified in standardized test chambers (ISO 10140, 2010; ASTM E90-09, 2016). Standardized test methods employ continuous noise signals to excite the sending room. The sound insulation is determined through averaged sound level differences between the sending and receiving rooms with a correction term taking into account absorption in the receiving room. High insulation elements often post challenges for reliable measurement results since insufficient signal-to-noise ratios in the receiving room make the measurement inaccurate, often invalid. This paper discusses advantages of measurement techniques using pseudo random noise and /or log-sweep sine signals followed by efficient cross-correlation processing, leading to room impulse responses. Energy building of room impulse responses measured at microphone positions in both rooms also yields spatially averaged differences of sound energy levels. In addition, the room impulse responses measured in the receiving rooms also provide reverberation times to evaluate overall room absorption. Due to cross-correlation, the room impulse responses even in low signal-to-noise situations can be measured with drastically improved quality, yielding more reliable evaluation of level differences. This paper highlights theoretic fundamentals of correlation methods, their equivalence, and differences with the classical noise excitation method.